M
MAGMATISM AT CONVERGENT PLATE
BOUNDARIES
Robert J. Stern
Department of Geosciences, University of Texas at Dallas,
Richardson, TX, USA
Synonyms
Arc magmatism; Island arc; Magmatism; Subduction zone
magmatism
Definition
Convergent margin magmatism – also called arc
magmatism – occurs at straight or curved alignments
(arcs) of discrete volcano-plutonic complexes that form
above a subduction zone, where oceanic plate material
(lithosphere plus sediments) is recycled into Earth’s mantle (Figure 1). Convergent plate margins are one of the two
types of plate boundaries where abundant igneous activity
is caused by plate tectonics (the other is associated with
divergent plate boundaries or mid-ocean ridges (MOR);
hot-spot or within-plate igneous activity may be related
to mantle plumes). Convergent margins and associated
igneous activity occur in three regions: (A) around most
of the Pacific Ocean (circum-Pacific Ring of Fire),
(B) along much of the southern margin of Eurasia; and
(C) in two short arcs in the western Atlantic
Ocean (Figure 2).
Principal Components: Convergent margins are
subdivided into forearc, volcanic front, and backarc
(Figure 1) with increasing distance from the plate boundary, marked by the trench. Forearcs are stable regions
underlain by cool mantle, in contrast to the volcanic front,
which is underlain by hot mantle. Forearc crust is generated when the subduction zone first formed and is often
emplaced on land as ophiolite (Stern et al., 2012).
Accretionary Wedges are found only for active continental
margins with high sedimentation rates. Island arc magmatic activity is concentrated at the volcanic front
(sometimes called the magmatic front, because not all
magmas erupt), defined as the locus of the first volcanoes
inboard from the trench. Some island arcs are under tension. Extension can be so strong that true seafloor spreading occurs, forming a backarc basin (Taylor, 1995).
Backarc basins are entirely submarine, lying ~2–5 km
below the sea surface. Actively spreading backarc basins
are associated with the Aeolian, S. Sandwich, TongaKermadec, New Hebrides, Andaman-Nicobar, and
Mariana arcs, and are also found in the western Mediterranean Sea (Figure 2). Many marginal seas originated as
backarc basins. Active backarc basin spreading ridges
erupt basalts that are similar in composition to those
erupted at mid-ocean ridges except for containing much
higher concentrations of magmatic water and fluid-mobile
trace elements. In contrast to subduction zones and associated island arcs, which remain active for several tens or
even hundreds of millions of years, backarc basins stay
active for only 10–20 million years, perhaps because continued widening due to seafloor spreading eventually separates the region of mantle upwelling from subductionrelated water inputs needed for melt generation (Stern
and Dickinson, 2010). Interarc rifts also can be found
where island arcs experience extension, but not to the
point of seafloor spreading. Interarc rifts are associated
with the Ryukyu, Izu, and Aegean arcs.
Subduction zone and mantle wedge processes
Generally built above a dipping zone of earthquakes, convergent margin magmatism demonstrates that a subduction zone operates deep beneath a region. Subduction
zones mark the subsurface expression of convergent plate
boundaries, one of the three main types of plate tectonic
boundaries, the others being divergent and transform plate
J. Harff et al. (eds.), Encyclopedia of Marine Geosciences, DOI 10.1007/978-94-007-6238-1,
© Springer Science+Business Media Dordrecht 2016
MAGMATISM AT CONVERGENT PLATE
BOUNDARIES
Robert J. Stern
Department of Geosciences, University of Texas at Dallas,
Richardson, TX, USA
Synonyms
Arc magmatism; Island arc; Magmatism; Subduction zone
magmatism
Definition
Convergent margin magmatism – also called arc
magmatism – occurs at straight or curved alignments
(arcs) of discrete volcano-plutonic complexes that form
above a subduction zone, where oceanic plate material
(lithosphere plus sediments) is recycled into Earth’s mantle (Figure 1). Convergent plate margins are one of the two
types of plate boundaries where abundant igneous activity
is caused by plate tectonics (the other is associated with
divergent plate boundaries or mid-ocean ridges (MOR);
hot-spot or within-plate igneous activity may be related
to mantle plumes). Convergent margins and associated
igneous activity occur in three regions: (A) around most
of the Pacific Ocean (circum-Pacific Ring of Fire),
(B) along much of the southern margin of Eurasia; and
(C) in two short arcs in the western Atlantic
Ocean (Figure 2).
Principal Components: Convergent margins are
subdivided into forearc, volcanic front, and backarc
(Figure 1) with increasing distance from the plate boundary, marked by the trench. Forearcs are stable regions
underlain by cool mantle, in contrast to the volcanic front,
which is underlain by hot mantle. Forearc crust is generated when the subduction zone first formed and is often
emplaced on land as ophiolite (Stern et al., 2012).
Accretionary Wedges are found only for active continental
margins with high sedimentation rates. Island arc magmatic activity is concentrated at the volcanic front
(sometimes called the magmatic front, because not all
magmas erupt), defined as the locus of the first volcanoes
inboard from the trench. Some island arcs are under tension. Extension can be so strong that true seafloor spreading occurs, forming a backarc basin (Taylor, 1995).
Backarc basins are entirely submarine, lying ~2–5 km
below the sea surface. Actively spreading backarc basins
are associated with the Aeolian, S. Sandwich, TongaKermadec, New Hebrides, Andaman-Nicobar, and
Mariana arcs, and are also found in the western Mediterranean Sea (Figure 2). Many marginal seas originated as
backarc basins. Active backarc basin spreading ridges
erupt basalts that are similar in composition to those
erupted at mid-ocean ridges except for containing much
higher concentrations of magmatic water and fluid-mobile
trace elements. In contrast to subduction zones and associated island arcs, which remain active for several tens or
even hundreds of millions of years, backarc basins stay
active for only 10–20 million years, perhaps because continued widening due to seafloor spreading eventually separates the region of mantle upwelling from subductionrelated water inputs needed for melt generation (Stern
and Dickinson, 2010). Interarc rifts also can be found
where island arcs experience extension, but not to the
point of seafloor spreading. Interarc rifts are associated
with the Ryukyu, Izu, and Aegean arcs.
Subduction zone and mantle wedge processes
Generally built above a dipping zone of earthquakes, convergent margin magmatism demonstrates that a subduction zone operates deep beneath a region. Subduction
zones mark the subsurface expression of convergent plate
boundaries, one of the three main types of plate tectonic
boundaries, the others being divergent and transform plate
J. Harff et al. (eds.), Encyclopedia of Marine Geosciences, DOI 10.1007/978-94-007-6238-1,
© Springer Science+Business Media Dordrecht 2016